Preview stage¶

Preview answers four questions: which layers are visible, what each color means, where the current move sits, and whether the result is safe to export.

flowchart LR
  G["Generated or parsed toolpath"] --> L["Choose layer band"]
  L --> C["Choose color-by field"]
  C --> S["Scrub moves and inspect HUD"]
  S --> F["Open findings or compare ghost"]
  F --> E["Export generated path"]

Layer band¶

PROPOSED — the current single vertical slider becomes a dual-range slider:

HOW IT IS — both apps currently mount a single LayerSlider (src/SlicerApp/MainWindow.axaml:26–28; src/SimulatorApp/MainWindow.axaml:24–26). The Slicer routes changes through SetLayerVisibility and buffer rebuild (src/SlicerApp/MainWindow.axaml.cs:741–751; src/Nps.Shell/ViewportController.cs:252–257,657–661). Parsed paths already grow the single slider from their real move layers (src/SlicerApp/MainWindow.axaml.cs:477–500). The ABI’s direct ViewportGetLayerCount query exists but has no production UI consumer (src/Nps.EngineHost/NpsAbi.cs:408–409).

Color by¶

PROPOSED — one toolbar dropdown becomes the single home for color mapping; the Overlays inspector mirrors the same selection. The contract names eight UI ids:

HOW IT IS — selecting one of the five current radios calls the one-shot ViewportApplyOverlay path and updates legend range/stats (src/Nps.Shell/ViewportController.cs:517–547,564–639). The dropdown and three non-planar ids are PROPOSED. The dropdown is populated through the existing, currently unconsumed GetSupportedOverlayIds export (src/Nps.EngineHost/NpsAbi.cs:467–474).

Display toggles¶

These are display filters. They do not regenerate or change exported G-code.

Interactive legend¶

PROPOSED — the legend extends the current range display:

• Click a legend class to show or hide it.
• Hover a class to see its move/time fraction.
• Keep units, low/high values, and inversion visible.
• Use viewport-content color ramps, not new chrome colors.

HOW IT IS — OverlayPanel already displays low/high labels, a gradient, and stats text (src/Nps.Shell/Controls/OverlayPanel.axaml:15–35). Clicking and hovering legend entries are PROPOSED.

Statistics HUD and status estimates¶

PROPOSED — a left-sidebar section in Preview shows:

The same time and filament summary appears in the status bar. Both depend on a new additive GetLastGcodeStats(NpsGcodeStats) export. Until that export exists, the UI shows --; it must not invent estimates.

Time / move scrub¶

PROPOSED — a horizontal scrubber at the viewport bottom moves the playhead without creating a third simulation model. It uses the same ViewportSetSimulationState path as playback.

HOW IT IS — the Simulator scrubber already commits a move index through SetSimulationState and rebuilds buffers (src/SimulatorApp/MainWindow.axaml.cs:850–866). Pressing it pauses playback and release resumes only if playback was previously running (src/SimulatorApp/MainWindow.axaml.cs:868–915). Preview promotes that engine path to a stage-level scrub surface; Slicer has no scrubber today.

Ghost compare¶

PROPOSED — Ghost Compare shows a dim planar baseline under the active non-planar path:

1. Snapshot the active non-planar move spans in the host.
2. Regenerate a baseline with enableNonPlanar=0.
3. Snapshot the baseline before any later generation invalidates the engine buffer.
4. Restore/present the active path and draw the baseline in a second painter pass.
5. Scrub curved layers to inspect stair-step reduction.

Dirty banner¶

PROPOSED — after a generated path exists, the host stores a snapshot hash of slice and non-planar settings. A later edit produces a full-width banner:

Settings changed since last slice — Re-slice · Dismiss

The titlebar CTA changes from Slice to Re-slice. Dismiss hides the banner but does not mark the result current. Loading parsed G-code does not create a fake “slice settings” relationship.

Post-slice offer¶

PROPOSED — successful generation creates a non-blocking toast:

Slice complete — View Preview

The toast auto-dismisses and never forces a stage change. Failed or zero-move generation produces an error/status state, not a success offer.

Export¶

PROPOSED — Export is enabled only for a path generated in the current session. Parsed external G-code remains inspectable but Export is disabled with the reason “Nothing generated in this session.”

The export dialog:

• shows target filename and a size/preflight result;
• repeats the DEMO TOOLPATH warning when the visible generated path is demo;
• writes through existing WriteGcodeToFile;
• records success or failure in Activity;
• never relabels a demo path as a production slice.

WriteGcodeToFile and GenerateGcodeToBuffer already exist as ABI exports (src/Nps.EngineHost/NpsAbi.cs:347–359) but have no production UI consumer. The planned export dialog consumes them for preflight and final write. See Honesty for the provenance state machine.

Toolbar additions¶

HOW IT IS — the current toolbar has ten controls: five camera presets, Zoom to Fit, travels/extrusions toggles, and layer up/down (src/Nps.Shell/Controls/ViewportToolbar.cs:29–38,53–67).

PROPOSED — Preview adds Color by, Ghost, Paint, and a clip-plane slider. Clip requires an additive ViewportSetClipPlane export; it is not presented as working before that export lands.

See also¶

• Non-Planar controls for the three planned overlay ids and ghost verification.
• Honesty for generated-versus-parsed provenance and export warnings.
• Slicer — interaction map for today’s preview controls.
• Simulator — interaction map for today’s scrubber and overlays.